Method for the manufacture of compressed boards

ABSTRACT

The object of the present invention is a method of producing compressed boards by the hot pressing of board preforms from particles treated with a thermosetting binder. The field of use is primarily for the manufacture of wood chip boards,but other fields are also important.

United States Patent 11 1 Wirz l l Oct. 2, 1973 METHOD FOR THEMANUFACTURE OF COMPRESSED BOARDS inventor: Walter Wirz, Thalwil, Cantonof Zurich, Switzerland Assignee: Peter Fahrni, Head of Fahrni lnstitute,Ltd., Zurich, Switzerland Filed: Oct. 14, 1971 Appl. No.: 189,223

Foreign Application Priority Data Oct. 15, 1970 Switzerland 15227/70U.S. Cl 156/622, 156/626, 156/628,

264/128 Int. Cl B29j 5/04, B29j 5/02 Field of Search 156/622, 62.4,62.6,

[56] References Cited UNITED STATES PATENTS 3,301,726 1/1967 Matsukatu156/622 3,428,505 2/1969 Sicmpclkamp... 156/622 3,563,844 2/1971 Brown156/622 X Primary Examiner-Edward G. Whitby Attorney1ames M. Heilman etal.

[57] ABSTRACT The object of the present invention is a method ofproducing compressed boards by the hot pressing of board preforms fromparticles treated with a thermosetting binder. The field of use isprimarily for the manufacture of wood chip boards,but other fields arealso important.

8 Claims, 3 Drawing Figures METHOD FOR THE MANUFACTURE OF COMPRESSEDBOARDS The object of the present invention is a method of producingcompressed boards by the hot pressing of board preforms from particlestreated with a thermosetting binder. The field of use is primarily forthe manufacture of wood chip boards, but other fields are also moldline, whereby a lot of space is taken up and the plant is madecomplicated in development and opera tion. Furthermore, the sheetsbecome worn. Their thickness must therefore be checked periodically andthey must be replaced from time to time. Finally, the change in thethickness of sheet by wear must be taken into consideration upon thepressing These disadvantages are particularly evident when flexiblemetal screens are used, in accordance with a previously known method,instead of press sheets.

It has, to be sure, been proposed to strew the particles onto conveyorbelts or other supports which are not conducted into the main press andto separate the preforms from said supports for the charging of the mainpress and conduct them by special carriers into the heated main press.Such a procedure is, to be sure, not entirely without danger for thesensitive preforms. The transfer of the preforms from the conveyorsupports to so-called charging trays or the like frequently leads to achange in the structure of the preforms and thus to defective boards.

The above-described disadvantages are, inter alia, eliminated by thepresent invention. In the method of the invention, this goal is achievedin the manner that first of all webs which are thin with respect to thethickness of the board preforms are formed from particles, whereuponsaid webs are compacted by hot-pressing to such an extent that thebinder is at least partially set, and that thereupon the individualboard preforms are formed by strewing the particles onto these thin supporting layers which have been precompacted in this manner and theboards are produced by hot-pressing and combination of supporting layersand board preforms.

It has been found that even very thin support layers which have beensubjected merely to a brief hotpressing have a sufficiently highstrength to transport the preforms from the strewing points up into themain press without change in their internal structure. Furthermore, ithas been found that the thin, semicardboard or cardboard-like supportlayers combine in the heated main press with the other particle materialwhich is still loose at the start of the pressing process to formcompact bodies. This is true in particular when the upper sides of thesupport layers are strewn with a liquid or powder binder before thestrewing on of the particles which form the preforms.

The method also leads to further advantages. Aside from thesimplification of the forming line and the gen tle treatment of thepreforms while they are still loose, it has been found that, forinstance, the wear of the conveyor belts is also less since it is nolonger necessary to use guide rollers of very small diameter.Furthermore, the tolerances as to thickness are now only de pendent onthe press-plates. It is also favorable that hardening of the binder ofthe lowermost layer of the preforms, due to the contact heat of the hotcompressed boards, can, for all practical purposes, no longer takeplace. The support layers which have been very rapidly hot-pressed in aprevious stage of the process insulate the board preforms to a certainextent against the transfer of heat until the press is substantiallyclosed.

The present invention also relates to an apparatus for the carrying outof the new method. This apparatus is characterized by a strewing devicefor the formation of thin webs of particles intended for a surfaceregion of the boards, a hot press for compacting said webs to form thinsupport layers, further means for the strewing of the actual boardpreforms and a heated main press for the final pressing of the preformsand the combining thereof with the hot pre-pressed support layers.

There is described below by way of example the can rying out of themethod for the production of threelayer wood chip boards and an exampleof an embodiment of the apparatus, with reference to the drawing, inwhich:

FIG. 1 is a schematic side view of the installation.

FIG. 2 is a detail on a scale larger than FIG. 1, and

FIG. 3 is another detail, also on a scale larger than FIG. 1. i

l is a strewing machine which acts at the same time as supply bin. It isequipped at its lower end with two slinger rollers 2 covered with prongsand rotating in opposite directions. As a result of the rotation of theslinger rollers 2, fine top-layer chips are strewn onto anintermittently driven steel belt 4 which rotates over rollers 3. Thisbelt 4 extends through a heated press consisting of a press table 5 anda raisable and lower' able hydraulically driven press plate 6. Thestrewing machine 1 also acts intermittently. In fact, the slingerrollers 2 rotate only as long as the belt 4 is driven. The nip presentbetween the two rollers 2 and the speed of rotation of the rollers areso adapted to each other that a thin web of top-layer chips is formed onthe belt 4. In order that the thin support layer produced from the thinweb will, in contradistinction to the lower side, not be smooth on itsupper surface but will have a certain roughness which facilitates thebonding to the other chips in the main press, there is furthermoreprovided an endless metal screen 9 which travels in the form of a beltover guide rollers 8. One additional advantage of this screen resides inthe easy possibility of the removal of the steam produced upon the hotpressing.

The thin support layers which are produced in sections in endlesssequence, which layers are smooth on the one side and rough on the otherside, and may correspond with respect to thickness and flexibilityapproximately to relatively thin cardboard sheets, are now cut by meansof an automatic cutter 11 into pieces 13 of equal length. These piecesare then taken over by a conveyor belt 12 and so arranged in a row thattheir ends overlap over a certain distance. In this connection as can benoted in particular from FIG. 2 the overlap is always of such a naturethat the rear end of each support layer lies above the front section ofthe next following support layer.

Another conveyor belt leads the intermittently fed support layers withuniform speed to the strewing machines and 22. In front of said strewingmachines there is provided a unit for the spraying of a relativelyliquid binder onto the upper rough surfaces of the support layers 13.The spraying apparatus consists essen tially of a nozzle 16, a feed pump17 and a supply container 18. The spraying of the precompacted supportlayers improves the adherence to the rest of the chips. Of course, thewood chips discharged by the strewing machines 1, 20 and 22 have beenpreviously treated in known manner with a thermosetting binder.Furthermore, it should be pointed out that the precompacting of the thinsupport layers which are active as strewing, transporting and presssupports in the example described need not necessarily be effected allthe way to complete hardening of the binder. In many cases it issufficient for the binder to be only partially hardened.

The final polymerization can then take place in the main press, which isnot shown in the drawing.

The supply container of the strewing machine 20 contains coarser woodchips which are intended for the formation of the center or core layerof the three-layer boards to be produced. At its lower end the saidcontainer is closed off by two slinger rollers 21 rotating in oppositedirection. These rollers throw the core-layer material onto the endlesssequence of precompacted support layer 13 which have been provided witha thin film of glue. Behind the srrewing machine 20 there could, ofcourse, also be provided vertically adjustable dosaging means, such as,for instance, a combing dosaging roller or the like. The supplycontainer of the strewing machine 22 which is equipped with slingerrollers 23 contains top-layer chips ofthe same type as the container ofthe strewing machine 1. These chips are now strewed onto the core-layerchips, whereby an endless board preform 24 is formed.

A longitudinally and transversely movable, automatically acting partingsaw 25 whose shaft 26 is driven in a manner not shown in detail cuts theweb 24 which has thus been formed into sections of equal length whichcorrespond to the length of the wood chip boards to be produced. In thisconnection it should be seen to it that on the one hand the precompactedsupport layers are not cut and on the other hand that the cuttingprocess takes place in each case in the vicinity of the rear edge ofeach support layer 13 (see FIG. 2).

From FIG. 3 it can finally be seen how the board preforms are conveyedfurther by means of a conveyor belt 27 which is periodically driven witha speed which is greater than the speed of the conveyor belt 15. Uponthe taking over by the conveyor 27, there occurs a separating in spaceof the board preforms which have been cut to given lengths. The supportlayers 13 with the preforms 24 lying thereon are now conducted into theheated main press (not shown in the drawing) in which the boards areimparted their final shape by the compressing of the chip material andthe combining thereof with the support layers 13 which act assubstrates.

Due to the described manner of arranging the support layers 13 onebehind the other and a proper selection of the line of cut upon thecutting of the still loose preforms, there is produced in connectionwith each support layer 13 a front section as seen in the direction ofmovement which is not covered with particles. In

this way one has the possibility of grasping the charged support layersby means of grippers and in this way pulling them over a fixed support.For example, the preforms 24 can be conveyed in this manner into themain press, in which connection the support layers can then themselvesbe used as actual transportation supports in the same manner as thegenerally known transportation plates.

Mention should also be made of the fact that in certain cases anuninterruptedly operating, continuous press can suitably be used aspress for producing the precompacted support layers. Furthermore, otherpresses can also be employed, such as suitably heated roller presses,etc. The new method is therefore in principle not dependent on whetherthe plant operates intermittently or continuously. The expression boardpreform is accordingly to be understood in its broad est sense. Itcomprises both endless webs and discrete web lengths. Furthermore, theinvention can be employed, regardless of whether the board preforms havebeen subjected to a prior cold-pressing or not. In addition, the methodof the invention can be carried out in connection with single-layer andmulti-layer boards. In the example described, the pre-compacted supportlayer forms the bottom outer layer of the board. This need notabsolutely be the case. One could possibly also prefabricate supportlayers which represent merely a part of the lower outside layer. In suchcase, one would, to be sure, be forced to strew further top-layermaterial onto the pre-prepared support layers before applying thecore-layer material. Finally, the precompacting of the thin webs couldbe utilized also for other purposes, for instance by the application offireretarding addition substances, antifungus agents or the like ontothe pre-prepared support layers.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as fol lows:

1. Method of producing compressed boards by hot pressing of boardpreforms consisting of particles treated with a thermosetting binderparticularly for the manufacture of wood chip boards characterized bythe fact that initially webs, which are thin as compared with thethickness of the board preforms, are formed from particles whereuponthese webs are compacted by hot pressing to such an extent that thebinder is at least partially set, and that thereupon the board preformsproper are formed by the strewing of particles onto these thin supportlayers which have been precompacted in this manner, and the boards areproduced by hot pressing and combining of support layers and of boardpreforms.

2. Method according to claim 1 characterized by such a hot pressing ofthe thin support layers that the lower side becomes smooth and the upperside rough. 3. Method according to claim 1 characterized by the factthat the hot pressing of the thin support layers is interrupted beforethe binder, with which the particles have been treated, has been cured.

4. Method according to claim 1 characterized by the fact that the uppersides of the thin support layers are strewn with a liquid or pulverulentbinder before the strewing of the particles intended for the formationof the board preforms.

5. Method according to claim 1 for the manufacture of multi-layer boardswith top layers of particles which are thinner than the core layermaterial characterized by the fact that for the formation of theprecompacted support layers there is used a part of the particlesprovided for the production of the lower outer layer.

6. Method of producing compressed boards by hot pressing of boardpreforms consisting of particles treated with a thermosetting binderparticularly for the manufacture of wood chip boards characterized bythe fact that initially webs,which are thin as compared with thethickness of the board preforms, are formed from particles whereuponthese webs are compacted by hot pressing to such an extent that thebinder is at least partially set, and that thereupon the board preformsproper are formed by the strewing of particles onto these thin supportlayers which have been precompacted in this manner, and the boards areproduced by hot pressing and combining of support layers and of boardpreforms, and characterized by the fact that the precompacted supportlayers serve as strewing, transporting, and pressing supports for theboard preforms; and further characterized by the fact that the supportlayers charged with the board preforms are pulled by means of grippersof a conveyor device over a stationary support. 12

7. Method according to claim 6 characterized by the fact that theprecompacted support layers are arranged in a row alongside of eachother before the formation of the actual preforms in such a manner thatthe support layers partially overlap, and that after the strewing of anendless preform the latter is so cut that, after the pulling apart ofthe support layers. a front section, seen in the direction of movement,of each support layer is not covered with particles.

8. Method of producing compressed boards by hot pressing of boardpreforms which include particles mixed with a thermosetting binderincluding the following steps: spreading fine particles mixed with athermosetting binder on a base at a first position and compacting by hotpressing to partially set the binder, thereby forming a series ofsupport layers; transporting said lay ers to a second position andproducing a partial overlap of the layers adjacent their ends; spreadingcoarse particles mixed with a thermosetting binder on said layers toproduce an endless preform; spreading fine particles on the coarseparticles; cutting the coarse and fine layers at a position adjacent theoverlap of the base layers; pulling the base layers apart; and hotcompacting the separated boards to produce a series of particle boardscompacted with a fully set thermosetting binder.

2. Method according to claim 1 characterized by such a hot pressing ofthe thin support layers that the lower side becomes smooth and the upperside rough.
 3. Method according to claim 1 characterized by the factthat the hot pressing of the thin support layers is interrupted beforethe binder, with which the particles have been treated, has been cured.4. Method according to claim 1 characterized by the fact that the uppersides of the thin support layers are strewn with a liquid or pulverulentbinder before the strewing of the particles intended for the formationof the board preforms.
 5. Method according to claim 1 for themanufacture of multi-layer boards with top layers of particles which arethinner than the core layer material characterized by the fact that forthe formation of the precompacted support layers there is used a part ofthe particles provided for the production of the lower outer layer. 6.Method of producing compressed boards by hot pressing of board preformsconsisting of particles treated with a thermosetting binder particularlyfor the manufacture of wood chip boards characterized by the fact thatinitially webs, which are thin as compared with the thickness of theboard preforms, are formed from particles whereupon these webs arecompacted by hot pressing to such an extent that the binder is at leastpartially set, and that thereupon the board preforms proper are formedby the strewing of particles onto these thin support layers which havebeen precompacted in this manner, and the boards are produced by hotpressing and combining of support layers and of board preforms, andcharacterized by the fact that the precompacted support layers serve asstrewing, transporting, and pressing supports for the board preforms;and further characterized by the fact that the support layers chargedwith the board preforms are pulled by means of grippers of a conveyordevice over a stationary support.
 7. Method according to claim 6characterized by the fact that the precompacted support layers arearranged in a row alongside of each other before the formation of theactual preforms in such a manner that the support layers partiallyoverlap, and that after the strewing of an endless preform the latter isso cut that, after the pulling apart of the support layers, a frontsection, seen in the direction of movement, of each support layer is notcovered with particles.
 8. Method of producing compressed boards by hotpressing of board preforms which include particles mixed with athermosetting binder including the following steps: spreading fineparticles mixed with a thermosetting binder on a base at a firstposition and compacting by hot pressing to partially set the binder,thereby forming a series of support layers; transporting said layers toa second position and producing a partial overlap of the layers adjacenttheir ends; spreading coarse particles mixed with a thermosetting binderon said layers to produce an endless preform; spreading fine particleson the coarse particles; cutting the coarse and fine layers at aposition adjacent the overlap of the base layers; pulling the baselayers apart; and hot compacting the separated boards to produce aseries of particle boards compacted with a fully set thermosettingbinder.